The present invention relates to imaging apparatus and controlling method thereof having an optical system using the characteristics of a variable configuration mirror (also referred to as deformable mirror or flexible mirror).
Generally, the entire size and performance of an imaging equipment such as a camera or display equipment are likely to depend on its optical system. In order to improve performance not only of a camera but also of other imaging equipment or display equipment, especially to improve the performance concerning downsizing and power saving, therefore, the optical system is always required to be reduced in size and power consumption. Such demands are intense especially in the field of digital camera and mobile phone's camera unit, i.e., digital imaging equipment. Variable configuration mirrors have been proposed for example in Japanese patent application laid-open No.11-317894 and Japanese patent application laid-open No.2002-122784 as the means for achieving a reduction in size and power consumption of the optical system.
An example of the variable configuration mirrors proposed in the abovementioned documents will now be described by way of FIGS. 1A and 1B. FIG. 1A is a top view, and FIG. 1B is a sectional view along X-X′ of FIG. 1A. As shown in FIGS. 1A and 1B, a variable configuration mirror 101 has a ring-like support wall (spacer) 103 projected from one end surface of a disk-like base plate 102, and fixed electrodes consisting of one center electrode (first electrode) 104A and two peripheral electrodes (second and third electrodes) 104B, 104C are disposed within a region surrounded by the ring-like support wall 103. A peripheral portion of a mirror body (movable electrode) 105 is then joined and fixed to the opening end of the ring-like support wall 103.
The two peripheral electrodes 104B, 104C each are made of an electrode plate in the form of a half circular arc disposed substantially in a 180-degree angular range. The center electrode 104A is formed as a disk-like electrode plate disposed within the circular region occurring at the center portion of the two peripheral electrodes 104B, 104C. It should be noted that the fixed electrodes are made for example of chromium and that the pattern thereof is not limited to the one illustrated and various other forms can be suitably used. The mirror body 105 is formed for example such that aluminum serving as both a movable electrode and a reflecting member (mirror surface) is adhered to an outer surface of a circular disk which is formed of a polyimide resin.
When a predetermined voltage is applied between the fixed electrodes (104A to 104C) and the movable electrode (mirror body 105) of thus constructed variable configuration mirror 101, the curved configuration of the reflecting surface (mirror body 105) is variably controlled by the electrostatic force thereof. Accordingly, the voltage is controlled from an external source so as to result in a suitable curvature of the reflecting surface.
A description will now be given by way of FIG. 2 with respect to an example of the construction of a drive section of thus constructed variable configuration mirror. Referring to FIG. 2: numeral 111 denotes a booster circuit for increasing a power supply voltage (3.3V for example) to a maximum voltage (100V for example) to be applied to the fixed electrodes of the variable configuration mirror; and numeral 112 denotes a driver for setting the respective application voltages to the fixed electrodes (first to third electrodes 104A to 104C) of the variable configuration mirror, constituted in this example by three driver circuits so as to be able to drive the variable configuration mirror 101 which has three fixed electrodes. Numerals 113A to 113C denote first to third switching devices each constituted by FET, connected at one end thereof to the output VOUT1 to VOUT3 of the respective driver circuits and at the other end thereof to the respective fixed electrodes 104A to 104C of the variable configuration mirror 101.
In thus constructed drive section, ON/OFF of each switching device 113A to 113C is controlled by control voltage VSW to be commonly applied on the control terminals of the respective switching devices 113A to 113C. When the switching devices 113A to 113C are controlled to be ON, voltages VOUT1 to VOUT3 set at the respective driver circuits are applied on the respective fixed electrodes 104A to 104C so that the movable electrode (mirror body) can be variably controlled to a predetermined curved configuration.
Thus constructed variable configuration mirror is disposed within the optical system of a camera so that the curvature of the mirror body can be changed by controlling the applied voltage to adjust focal length thereof. It should be noted that the shape of the mirror body is not limited to a circular form, and an oval can also be used. The variable configuration mirror constructed as described has two distinct features: it is smaller in size and consumes less power as compared to the conventional lens optical system to be driven by motor; and, while a large motor sound and noise at transmitting system are caused in the conventional motor-driven lens optical system, the variable configuration mirror is substantially soundless.